"99 V70 XC 157,000 keeps getting stuck in reverse, what could it be?

 

Hello, I sure can be dense at times but a little more detail would help. Is it your gear selector lever getting stuck when trying to get out of "R"? Or, does the car stay in reverse when you move the lever to "D"?
There are posts on "rowing" your selector lever as part of a diagnosis. That action might clean the contacts in your PNP switch. If such rowing changes anything then you have narrowed the problem down a bit. There are posts on opening up the PNP switch and cleaning it. There are posts about changing it too. You can see it atop the transmission while looking down along the engine side of the air cleaner box. It is actuated by a cable which is connected to your gear selector lever.
Has your fluid been changed? There's a myth out there stating that the fluid is good for life. If your fluid is soooo dirty it's condition is impeding the operation of your transmission, a flush might be too late. Remember I have no data here. Since your 4-speed unit takes the cheap Dexron/Mercon fluid it would be informative to change the fluid if black.
Under no circumstances have your transmission "power flushed". Kira

 

Sorry when I put it in reverse the car doesn't move, feels like it is stuck in neutral then slowly moves into reverse but ever so slowly. I will try the rowing of the selector level. I did change the transmission fluid in the summer by drain and filling it.

 

Hello, When it finally goes into reverse, is it solidly in reverse? That is to say, will the car then respond to the gas peddle in reverse or will it chatter or fail to go, say, uphill in reverse? When you changed the fluid did you drain the sump only once? Did you take note of the condition of the fluid? Was it black and smelly? One thing you can be happy for is that if your unit needs a rebuild it is a cheap unit to fix, relatively speaking. Kira

 

When it goes into reverse it feels like it is going uphill. When I drained the fluid I did it slowly, a little at a time so it was never empty. Fluid was not black and smelly, more brownish red.